Some niche, specialised (except the last group), valuable, but relatively well-known YT channels for learning

Science:

Minute Physics https://www.youtube.com/@MinutePhysics

Minute Earth https://www.youtube.com/@MinuteEarth

Mathematics:

Numberphile https://www.youtube.com/@numberphile

3Blue1Brown https://www.youtube.com/@3blue1brown

History:

History Matter https://www.youtube.com/@HistoryMatters

Oversimplified https://www.youtube.com/@OverSimplified

Story writing:

Terrible Writing Advice https://www.youtube.com/@TerribleWritingAdvice

Philosophy:

Rational Animations https://www.youtube.com/@RationalAnimations
Exurb1a https://www.youtube.com/@Exurb1a

Multiple:

Khan Academy https://www.youtube.com/@khanacademy/videos

Crash Course https://www.youtube.com/@crashcourse

Veritasium https://www.youtube.com/@veritasium/videos

Kurzgesagt https://www.youtube.com/@kurzgesagt
CGP Grey https://www.youtube.com/@CGPGrey

Individual playlists from the above about self-help in particular:
Kurzgesagt https://www.youtube.com/playlist?list=PLveQG4rYZZUnIyXrWVlL8YHVjcxYxK1QQ

CGP Grey https://www.youtube.com/playlist?list=PLveQG4rYZZUlF7a1cKTcVxhJToqwtQt1g

These are the small, niche channels I can quickly list off. They do not necessarily reflect my beliefs, so I am not endorsing them in that sense, but they have useful information. Obviously, niche channels will tend to skew biased towards niche movements and beliefs, so do not ignore bigger channels if you decide to go down a rabbit hole.

Philosophy:

-https://www.youtube.com/@MajestyofReason

-https://www.youtube.com/@ParkersPensees

-https://www.youtube.com/@lizjackson111

-https://www.youtube.com/@thefreewillshow2132

-https://www.youtube.com/@WorldviewDesignChannel

-https://www.youtube.com/@owl235/

-https://www.youtube.com/@KaneB/

Politics:

-https://www.youtube.com/@bitbutter

-Bad YouTube channel, but good substack: https://www.youtube.com/@BryanDCaplan/

Biblical Scholarship:

-https://www.youtube.com/@SentinelApologetics

-https://www.youtube.com/@ancientegyptandthebible

YouTube is generally not a good source for these topics in particular, so I recommend using these channels to find good book and articles. Some of these channels are run by scholars, so check out their works. You can easily find their critics too.

Law channel focusing on tech and video games: https://www.youtube.com/@HoegLaw

Video game animation: https://www.youtube.com/@NewFramePlus/featured

Synthesizer music creation: https://www.youtube.com/@RedMeansRecording

Older philosophy channel: https://www.youtube.com/@pbsideachannel

https://www.youtube.com/@HBMmaster
Jan Misali, he's a guy who reviews conlangs as well as making videos on other assorted intellectual topics. My personal favorite video of his is this one on extended definitions of the regular polyhedra https://www.youtube.com/watch?v=_hjRvZYkAgA

https://www.youtube.com/@seseragistudio

Very valuable how, and to whom? David Bull's channel is great, I love it, has a lot of info you can't find anywhere else at all, but it is, as requested, very niche, so -

Do you want *really* unknown? https://www.youtube.com/@dambookswithfloydbeaver4457 is about classic books and it has a funny, high-effort presentation style.